原型设置中 this 的疑惑

[moliu]

function Collection(size)

{

this.size = function(){return size};

}



Collection.prototype.isEmpty = function(){ //这里的this指的是 Collection 还是 Collection.prototype ？

return this.size() == 0;//如果是Collection.prototype ，它能调用 Collection 的方法吗？

}//Collection.prototype 也是个对象啊

[moliu]

function Point(dimension)

{

this.dimension = dimension;

}

//定义一个Point2D类型，“继承”Point类型

function Point2D(x, y)

{

this.x = x;

this.y = y;

}

Point2D.prototype.distance = function()

{

return Math.sqrt(this.x * this.x + this.y * this.y);

}

Point2D.prototype = new Point(2); //经过上面的设置，new Point(2)有distance 属性了吗？

[zhangshaolongjj]

this指的是 new Collection（）的对象

[dh20156]

关于this的最终回复，参见ECMA-262 10.2.3：


The caller provides the this value. If the this value provided by the caller is not an object (including the case where it is null), then the this value is the global object.


其他的参见Javascript Scope Chain相关资料。

[moliu]

var B={m:5};
function A(){}
A.prototype=B;
A.prototype.z=8;
b=new A();
alert(b.z); //output 8
alert(b.m); //output 5
alert(B.z); //output 8
for(S in B)
document.write(S+"="+B[S])//m=5z=8